regex_pattern = r'^.{3}..{3}..{3}..{3}$'

we need to use ^ at the start and $ at the end as we search for exact match in the entire test_string

test_string must be in the required format and there is only one occurence of the required string we are searching for.

I hope I explain it well

either of these would do

regex_pattern = r"^(.{3}\.){3}.{3}$"	# Do not delete 'r'.
regex_pattern = r"^...\....\....\....$"

My regex:

^((?:[^\n]{3}.){3}(?:(?:[^\n]){3}))$

^(.{3}(.)){3}.{3}$

Shouldn't it be: ^\.{3}(\..{3}){3}$ because you want to match "..." followed by "\..." 3 times?

However, something like ^(\.?.{3}){4}$ would also match "..." repeated 4 times, e.g. "abcabcabcabc"? Unless I just misunderstood the question.